Gear finishing



y 9 I M. B. MENTLEY 2,318,179

1 GEAR gmxsanm Filed June 26. 1939 INVENTOR. MAX EMENTLEY i ATTO Patented May 4, 1943 UNITED STAT S PATENT OFFl'CE Max B. Mentley, Detroit, Mich, assignor to National Broaeh a Machine Company, Detroit,

Mich, a corporation of Michigan Application June 26, 1939, Serial No. 281,278

9 Claims.

The present invention relates to gear finishing and more particularly to a new method of modifying gear teeth. The present invention embodies the general type of gear finishing illustrated and described in Robert S. Drummond 2,126,178 of August 9, 1938.

Briefly reviewed for clarity, in this type of gear finishing a gear blank to be finished is run in mesh with a gear finishing tool. The gear finishing tool is in the form of a gear conjugate tothe gear blank and has teeth which are provided with working surfaces. These surfaces may be lapping surfaces or cutting surfaces, or the like. The present invention is more particularly concerned with tools having cutting surfaces, although, as will be evident as the description proceeds, the same invention may be practiced with somewhat less efficiency with lapping tools.

As set forth in the patent above referred to, it is preferred to position the gear and the tool with their axes crossed at a small angle. This results in limited contact between the teeth of the tool and of the gear with the result that cutting takes place with a minimum of pressure and accordingly with a minimum of distortion. In order to distribute the finishing action of the tool from end to end of the gear teeth, a relative motion is introduced by the gear and tool which is generally in a plane parallel to the axes of both.

The present invention contemplates the use of a special tool and the practice of a particular method to form gear teeth according to a desired form.

It has long been recognized that it is for practical purposes impossible to maintain a true lead when bobbing a relatively wide gear. This difficulty has been recognized to such an extent that wide gears have not been employed where conditions indicate they would be particularly useful.

The method of gear finishing disclosed in the above mentioned patent corrects numerous errors, and to some extent corrects lead. However, it

ployed, which is provided with cutting surfaces on one side only of its teeth, a novel finishing action and method may be practiced. The side of the teeth of the tool which are not provided with cutting surfaces serve as accurate guiding surfaces, and by feeding the gear relative to the tool in an appropriate manner, one side only of the gear teeth may be modified as desired. Then by reversing the gear relative to the tool and employing the just finished side of the teeth of the gear as the guiding surfaces, the other side of the gear teeth may then be cut to the desired form.

With the foregoing general remarks in'view, it is an object of the present invention to provide a novel method of finishing gear teeth.

It is a further object of the present invention to provide a'novel tool, useful in the method referred to.

More specifically it is an object of the present invention to provide a gear finishing tool having cutting surfaces on one side only of its teeth.

It is .a further object of the invention to finish gear teeth by a method which employs one side of the gear teeth as a datum surface while modifying the other side of the gear teeth in a predetermined manner therefrom.

It is a further object of the present invention to provide a method for finishing gears by means of .which the lead on one side of the gear teeth may be accurately controlled.

-It is a further object ;of the present invention to finish gears by a .method which enables the production of gear teeth having accurately predetermined'taper from end to end.

It is a further object of the present invention to provide a method for finishing gear teeth by means of which the lead or helix angle of the -gear teeth may be varied.

Other objects of the invention will be apparent as the description proceeds, and when taken in conjunction with the accompanying drawing,

has been found that this type of gear finishing,

as practiced, without further modification, isnot well adapted to correct lead as accurately as might be desired.

It should be mentioned at this time that in I the type of gear finishing disclosed in the patent,

one of the parts'either the gear or the tool, is positively rotated, whereas the other part is driven only through the intermeshing engagement of the gear and tool.- There is, therefore, a tendency for the teethof the tool to follow the false lead of a relatively wide gear.

- I have found that where a cutting tool is emwherein:

Figure l is a diagram illustrating the operation of the herein disclosed method;

Figure 2 is a fragmentary elevation of the tooth of a tool as used in the present invention; and

Figures 3, 4 and 5 are diagrammatic elevations indicating the relationship of parts in practicing the herein disclosed method.

Referring first to Figure 1 I have indicated diagrammatically the steps employed in the present method. Figure 1 may be considered as a developed View of a fragment of a gear, the tops of helical teeth in various stages of development,

being indicated at t1, ta, ta, t4.

We may assume for example that a helical gear has a number of teeth, such for example as t1. which upon measurement are found to have an error in lead of a certain amount. This error in lead may of course be expressed in degrees of helix angle,- but in practice is more conveniently measured in thousandths of an inch error from one end to the other. In the present case it is assumed that the tooth t1, as hobbed, has too great a helix angle, which it is desired to correct. The profiles of the teeth are measured from end to end and the amount of error is noted. As hobbed,

of course, the error in lead or helix angle will bethe same or practically the same on both sides of all teeth.

According to the present invention one side of the gear teeth will be employed'as a datum surface and will be used to guide the tool so as to modify the opposite surfaces of the teeth a predetermined amount.

For example, if it is desired to modify the teeth n so that they will retain their initial lead on the sides of the teeth indicated at a, while the lead on the opposite side of the gear teeth, for example at b, is to be changed in a direction to reduce the helix angle, by an appropriate meth od, which will subsequently be. described in detail, the sides of the teeth a are engaged by the sides of the tool which are not provided with cutting surfaces: the gear and tool are rotated and a relative feeding motion is introduced which will cause the predetermined desired modification of the sides b of the teeth. In the present case, for example, the tooth is will result, which has the sides a unmodified and which has the opposite side modified to a new profile b1, the

original profile I) being indicated in dotted lines.

For certain types of work it is desired to employ teeth which have different leads on opposite sides thereof, and therefore the present method may be employed to manufacture gear teeth having this characteristic. As a specific example, tapered teeth of this type are useful-where the gear is to be driven reversely and where the power twist between right-hand and left-hand rotation results in an off-angle spring of parts. This spring may result in the shafts of the driving and driven gear being at a slight angle during different hand rotation. This conditionmay be allowed for by providing opposite sides of one or both the gear and tool "with different leads or helix angles. If however it is desired to modify the lead or helix angle of the tooth m in a manner to reduce its helix angle, as for example to the form of the tooth to (shown in full lines), it is necessary only to invert or reverse the gear G relative to the same cutter and by appropriate feed to modify the second side of the gear teeth. It will be understood during modification of the second side of the gear, the first side of the gear teeth, which has already been modified, is employed as a guid-' ing surface.

Thus, for example, the tooth ti may have a lead which is found to be plus .005. By appropriate practice of the method heretofore briefly described, a tooth is may be formed on which the side b has been modified to a new lead or helix angle b, which is as desired. By then employing the sides In of the teeth as the guidin surfaces, the sides a of the teeth may be modified to a new profile m, which has the desired lead.

Referring more particularly. to the specific manners in which the above outlined method may be carried out, attention is now directed to Figembodiment of my invention, the axis ll of the gear G is inclined to the axis I! of the cutter C,

as shown in this figure. As will be recognized, the axis I! of the cutter C is shown in this figure as in a horizontal plane, but is rotated through a limited angle away from the plane of the paper. The gear G on the other hand is illustrated with its axis ii in the plane of the paper and therefore crossed at a limited angle to ,the axis it. In carrying outthe present invention, however, a second relative inclination is introduced by the axis I2 of the cutter C and the axis H of the gear G,'and this is indicated in Figure 3 by the angle 3:. It will be recognized that ii the gear G and the tool C are rotated in mesh, and if a relative feeding motion is introduced, such as would result from a translation of the gear G to the right in the direction of the arrow l4, tapered teeth will be produced on the gear G. It will further be recognized that all of the cutting acvtion is concentrated on one side of the gear teeth and that this cutting action is accurately controlled and guided by the guiding engagement between the uncut side of the gear teeth and the smooth or non-cutting side of the tool teeth. It will be evident that by the method 'Just described, the lead on one side only of all of the gear teeth may thus be changed by a definite amount. It will be understood, of course, that where the amount of change is sufficiently great, a number of relative translations will be employed and that there may be a relatively vertical feeding movement between the gear and tool between translations.

As previously mentioned, the gear as finished by the just mentioned operation may be useful in certain fields, and the method as thus far described is to be considered as complete in itself and as resulting in useful and novel production.

As an alternative to the method justde'scribed a second method may be employed which is diagrammatically illustrated in Figure 4. In this figure I have shown a cutter C adapted to rotate in the direction of the arrow shown and having an axis l2, which, as shown in this figure, is in a horizontal plane. The gear G in this instance may have its axis II also in a horizontal plane, but-as indicated in the figure, the axes i2 and II are crossed at a limited angle. In order to modify one side only of the teeth of the gear G, a relative feeding motion between the gear and tool may be introduced in the direction of the arrow it. It will be noted that this direction of feed is calculated to cause the axes of the gear and cutter to approach so that the cutter cuts deeper at one end of the gear than at the other. Due to the fact that the teeth of the cutter C are provided with cutting surfaces on only onesidethereof (in this figure again the lead surface) the tapered teeth will be formed by removing metal from one side only of the teeth.

In the two foregoing figures it will be appreciated that the amounts of inclination of the axes (Figure 3) and the direction of feed (Figure 4) are greatly exaggerated to clearly illustrate the method disclosed. As a matter of practice, the inclination or direction of feed varies very slightly from the horizontal. It will further be appreciated that while I have referred to directions of feed and of the axes as horizontal, this is done only for the purpose of convenience, and the only important limitation is the speciiic'relationship between the axes of the'gear and cutter, and the feed..-

Where it is desired to modify both sides of the gearteeth so as to provide teeth uniform from end to end by having a different lead from the original false lead, it is necessary only to carry the method one step further. As illustrated in Figure 5, in this figure the gear G is illustrated after it has been operated on according to the methods set forth in connection with Figures 3 and 4.

For the purpose of clearness, I have diagram-,

matically illustrated the teeth of the gear in Figure 5 as tapered from end to end. In this figure the teeth are indicated at l8; It will be understood that the gear G, as shown in Figure 5, is

therefore reversed relative to the cutter C from the position which it had in Figures 3 and 4'. In

into relatively wide tooth spaces, and that cutting action will therefore increase as a relative translation is introduced in the direction of the arrow 20. In this figure I have illustrated the axes i2 of the cutter and II of the gear as both disposed in horizontal planes, and the relative feeding motion takes place also in the horizontal plane.

As previously described, when the method is carried out as indicated in Figure 5, one side of the gear teeth has already been corrected for lead, and it is this surface of the gear teeth which contacts the non-cutting or guiding surface of the cutter tooth. As a result, when the operation illustrated in Figure 5 has been carried to the end to end of the gear, a gear results which has teeth of accurate predetermined lead from end to end.

Referring now particularly to Figure 2, the cutter which is employed in the present method is in the form of a gear having teeth 22 of a form conjugate to the teeth of the gear to be finished. The teeth of the tool are of a different helix angle from the teeth of the gear so that the two will mesh with their axes crossed at a limited angle. One face of the teeth 22 is provided with a plurality of grooves 23, leaving intermediate upstanding lands 24, each of which present sharp cuttin The sharp cutting edges 25 may be acute, right angles, or obtuse, and this will depend edges 25.

in part at least upon the helix angle of the cutter. Preferably the tooth is provided with an 011 clearance channel indicated at 26, illustrated and claimed in the prior Drummond patent and which forms no essential part of the present invention.

While the method disclosed herein has been described 'as primarily useful for modifying the lead of one or both sides of the gear teeth, it will be evident that it may be employed in a manner which will be evident to impart modifications of other gear characteristics to the teeth.

While I have illustrated and described but one specific embodiment of my invention, it will be apparent to those skilled in the art that various additions, modifications, omissions, combinations and substitutions may be made which will be within the spirit and scope of my invention as defined by the appended claims: 1

- tool so that the cutting surface of said tool i 3 What I claim as my invention is: I

1. The method. of altering the'lead on "gears which-comprises meshing a gear with a gearlike finishing toolhaving teeth provided with finishing surfaces on one side only, running saidgear and tool in mesh to remove metal from one side of said gear-teeth, reversing said gear rela- .tive to saidtool, and further running said gear and tool in mesh to remove metal from the other side of said gear teeth, v

2. The method of altering the lead on a gear which comprises meshing saidgear with a gearlike tool having teeth provided with cutting surfaceson one side only, with the axes of said gear and tool crossed, rotating said gear and tool and relatively moving said. gear and tool in a direction to remove more metal at one end of the gear teeth, relatively reversing saidgear and teeth contact the opposite side of said gear teeth,

' rotating said gear and tool, and relatively moving said gear and tool to form gear teeth.uni-

form from end to end and with an altered lead.

3. The method of altering the lead of gear teeth, which comprises meshing a gear with a gear-like tool having teeth provided with cutting surfaces on'one side only, .with the axes of said tool and gear crossed, rotating said gear and tool, relatively movingsaid gear and tool to distribute the cutting action of said tool from end to end of one side of said gear teeth and at the same .time causing the axes of-said gear and tool to approach, relatively reversing said gear and tool,

and relatively moving said gear and tool while] rotating in planes such that their axes remain uniformly spaced, to distribute the cutting action of said tool from en'd to end of the other side of said gear teeth.

point where the cutter has cut the teeth from 4. The method of forming tapered gear teeth which comprises meshing a gear with a gear-- like finishing tool having teeth provided with cuttingsurfaces on one side only, with the axes of said gear and tool crossed, rotating said gear and tool, and relatively feeding said gear and tool generally axially of saidgear in a direction to cause their axes to approach.

5. The method of finishing a gear which cornv prises providing a gear-like finishing tool havingteeth provided with cutting surfaces on one side i only and which has a different helix angle from the helix angle of said gear, meshing the gear and tool with their axes crossesd by an amount to allow for the difference in helix angle, providing a further relative-inclination of axes between said gear and tool tending to produce edge a bearing, and then translating said gear or tool in a plane parallel to the axes of said other while rotating said gear and tool.

e. The method of finishing a gear which com- 1 prises providing a gear-like finishing tool having teeth provided with cutting surfaces on one side only and which has a different helix angle from the helix angle of said gear, meshing the gear and tool with their axes crossed by an amount to allow for the difference in helix angle, rotate ing said gear and tool, and relatively translating said gear and, tool in a direction oblique to a plane parallel to the axes of both.

7. The method of correcting the lead of a gear which comprises meshing therewith a gear-like I I to'ol having teeth provided with cutting surfaces on one side only, rotating said gear or tool directly, and the other through their meshing engagement, and relatively translating said gear 1 and tool in a direction to cause their axes to vary in spacing, whereby metal will be removed in varying amounts from one side only of said gear teeth, relativly reversing said gear and tool, rotating said gear and tool, and relatively transiating said gear and tool with their axes uniformly spaced.

v 8. The method of. providing a lead on one side 0! gear teeth different from the lead on the other side which comprises, providing a gear-like rotary tool having teeth provided with cutting surfaces on one side only, meshing said gear and tool in tight mesh at crossed axes, rotating said gear and cutter by driving one directly and the other by intermeshing engagement, whereby tool teeth engage one side of the gear teeth in guid ing relation and engage the other side of said gear teeth in guided cutting relation, and relatively feeding said gear and tool in a direction to out said other side of said gear teeth to in- MAX B. MENTLEY. 

